Fragmentation regimes during the thermal interaction between molten tin droplet and cooling water

Abstract

A series of experiments was performed on the interaction between molten tin droplet with cooling water, and the experimental variables included initial temperature and falling height (impact velocity) of the droplet. At the initial stage of the interaction, a vapor film is formed immediately between the droplet and cooling water. Afterwards, it collapses locally owing to the Kelvin-Helmholtz instability and Rayleigh-Taylor instability. As the temperature of direct contact area between the droplet and cooling water is below the homogeneous nucleation temperature of water, the non-fragmentation regime occurs at the low-impact velocity of the droplet. The increased impact velocity of the droplet induces the sheet fragmentation which originates from the enhanced shear force acting on the droplet. As the temperature of direct contact area exceeds the homogeneous nucleation temperature of water, the honeycomb and granular fragmentation regimes are observed. The spiny structures are formed on the droplet surface by the rapid generation of local high vapor pressure in both regimes. The honeycomb fragmentation regime occurs at the low-impact velocity of the droplet. The direct heat transfer area is dramatically increased as the droplet impact velocity increases, resulting in the granular fragmentation regime. The granular fragmentation is affected by both the hydraulic factor (shear force) and the physical properties of molten tin.